Process for the preparation of Fumagilhn Fumagillin of the formula (1), a fermentation product of Aspergillus fumigata, is a potent antimicrosporidial agent. In its stable dicyclohexylamine salt form it is used in the veterinary medicine against microsporidiosis of bee and fish (Fumidil, Fumadil B, Amebicillin, etc). 
Fumagillin was recently found to be potent to cure intestinal infections caused by Microsporidia and/or Cryptosporidia in man (WO 96/30010). These infections are deadly diseases for patients with immunodeficiency.
Fumagillin, the monoester of decatetraenedioic acid and Fumagillol, is a very sensitive material. Due to its reactive groups (two epoxide groups capable for hydroxylation and ring opening; conjugated polyene-chain capable for dimerisation, polymerisation, epoxidation, hydroxylation; ester group capable for hydrolysis), Fumagillin is very sensitive to heat, air, light, acids, bases. It is considered to be stable at -80 xc2x0 C.
Fumagillin gives stable salts with amines containing bulky cycloalkyl substituents, like cyclohexylamine or dicyclohexylamine (the latter is used in the veterinary medicine). However, these amines are pharmaceutically not accepted in the human medicine as salt forming components, since they can accumulate in the tissues due to their lipofilic character. In addition, the Fumagillin dicyclohexylamine salt used in the veterinary medicine is of a purity of only 85%. (This means a Fumagillin content of only 61%).
To obtain Fumagillin, appropriate as a drug substance for human treatment, we aimed to prepare Fumagillin in pure form from the commercially available Fumagillin dicyclohexylamine salt, by a method which is also suitable for scaling-up. Purification of Fumagillin by recrystallization -subsequent to the liberation- is possible in small amounts, but it is not advisable in larger quantities, because of the sensitivity of the material to heat. Therefore, it was essential in our effort to obtain Fumagillin in pure condition directly from the liberation process, without further purification.
There is no reference to find in the literature for the preparation of pure Fumagillin from its salts.
The common method to obtain organic acids from their salts is liberation of the acid in aqueous medium by an inorganic or organic acid. As Fumagillin is sensitive to acids we used milder organic acids, i.e alkanecarboxylic acids of pKa 4.7 - 4.9 , in excess amount.
We carried out the liberation of Fumagillin from its dicyclohexylamine salt. with excess amount of acetic acid (pKa 4.76). The temperature of the aqueous reaction mixture was carefully maintained between 0-(+5) xc2x0 C. The precipitated Fumagillin, however, was not pure enough. It was therefore extracted with dichloromethane, the dichloromethane phase was washed with water, dried, concentrated in vacuo, and Fumagillin was precipitated from the concentrated solution on addition of methanol. The product thus obtained was pure, but it contained residual dichloromethane in high amount. The whole process was tedious, long and not appropriate for scaling-up. Yields varied between 45-60%, yields and also the quality of the product was not well reproducible.
To avoid the disadvantages of the above method we tried, liberations by alkanecarboxylic acids in organic media. Liberation in toluene was successful, however, dissolution of the salt on the effect of the acid was immediately followed by the precipitation of Fumagillin, allowing no possibility for a filtration, although filtration may be important. The product was not as pure as desired and its residual toluene content was high. Next we tried liberations in solvents or solvent mixtures of various ratio with the criterium, that a filtration has to be carried out during the process. We tried solvents such as toluene, alcohols, dichloromethane, acetonitrile, dioxane, acetone, ethyl acetate and their binary mixtures . Yields were medium to good. Residual solvent content of the products were also investigated.
The subject of our invention, in accordance with the above is a process for the preparation of Fumagillin by liberation from its salt characterized by reacting Fumagillin dicyclohexylamine salt with an organic acid in alcoholic medium. As organic acids, alkanecarboxylic acids with a pKa value of 4,7-4,9, preferably acetic acid, propionic acid, as alcoholic medium methanol, ethanol or propanol can be used The organic acid is preferably used in excess.
As a result of our process we have found that liberations in alcoholic medium gave surprisingly favourable results. The solution of the salt could be filtered, the acid was liberated from the clear solution. Yields were good, the product was pure. Residual solvent content in case of an alcohol is not critical, however, it is favourable that the products contained very little residual solvent. The process itself was mild, fast and well reproducible.
The most surprising result was that the Fumagillin samples obtained by this alcoholic method - probably due to their purity and low residual solvent content - turned out to be considerably more stable than the samples obtained by other methods. We carried out a 2-week stability study at 40 OC , ambient humidity, of selected samples obtained by various methods. The Fumagillin content of the samples was measured by HPLC before and after the stressing. Some demonstrative results are presented in the table below.
For liberation 3 equivalent of acetic acid were used in all demonstrated cases.
Thus, we have found a method yielding Fumagillin in high yield and pure condition; in ,addition the product obtained by this method turned out to be considerably more stable than products obtained by other preparation methods. Higher stability is a significant advantage in the case of such a sensitive drug substance.
The process itself is simple, fast, well reproducible, environment friendly and also appropriate for scaling-up.
Further details of the invention are demonstrated by the following examples, without limiting the claims to the examples.